Since sequences within the first intron of the alpha1(I) procollagen (Col1A1) gene may be involved in the formation of an active chromatin conformation, classical experiments using cultured cells and transgenic mice have not adequately resolved the function of the first intron in the cell-type-specific regulation of the Col1A1 gene. Consequently, the cell-type specific regulation of the Col1A1 gene will be studied within the context of the endogenous gene in order to take into account the influence of local chromatin conformation on gene expression. Deletions and mutations of specific elements within the first intron and promoter of the Col1A1 gene will be introduced into the endogenous mouse gene using the double replacement homologous recombination approach. The effect of the mutations on Col1A1 gene expression will be studied in the transgenic mice and in cell lines derived from these animals. Initially, a large portion of the first intron will be deleted to examine its significance in Col1A1 gene regulation within the context of the native chromatin structure. Subsequently, more subtle mutations that examine the function of specific elements within the intron will be introduced and tested.